Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications.
Traditional lighting installations, particularly in office spaces and other similar environments, have typically adopted a simple point-to-point connection methodology, where power is supplied to each luminaire via a dedicated, but essentially “free floating”, power cable. These power cables, which, in many regions, carry a high AC voltage, for example, 240V, typically hop from luminaire to luminaire, in a generally ad hoc manner, until all lamps are included in the system. In addition, each luminaire often requires the installation of a separate switch cable that connects each lamp or fitting to a dedicated control switch or bank of switches.
In a typical office lighting installation, luminaires are usually placed in a rectangular grid pattern, however, the cable routing above the ceiling, needed to supply these luminaire grids are by contrast very often quite irregular in their placement. In many cases the placement and routing of the power cables is left to the discretion of individual installers.
To help address this situation, a standard is being developed within an alliance called “EMerge,” an open industry association developing standards leading to the rapid adoption of DC power distribution in commercial buildings. The EMerge standard proposes the use of safe, low voltage (24V dc) power distribution and a more structured power supply scheme based on the use of rigid bus bars running above the ceiling. This system facilitates simplified and safe removal, connection, or re-location of lights in a lighting system. Also, because the bus bar system can be organized in a grid structure above the ceiling, it may be more suitable for connection with a luminaire grid that it provides power to. An example of a section of the proposed EMerge power supply bus bar, and the connectors needed to supply power to individual luminaires, and other devices in an office ceiling, are shown in FIG. 1.
Since the EMerge standard has been designed to make it easier for users to move and reconfigure lighting installations on-the-fly, it is desirable to ensure that luminaires can be easily associated and disassociated with control switches. To that end, EMerge proposes the use of wireless communications systems (currently ZigBee), rather than physical wires, to connect luminaires with user operated control points, for example, wall switches.
While traditional point-to-point style wiring strategies have very little impact on day-to-day use of office lighting installations, they present significant drawbacks regarding installing and commissioning lighting systems. Further, the point-to-point cabling used for an initial system may not be suitable for future modifications.
A major difficulty with commissioning any new lighting system is how to accurately map luminaires with control units or switches. For example, routing the wiring between a particular switch on the wall to the luminaire it controls in the ceiling. Traditionally the whole commissioning process is completely manual. The installer needs to first associate luminaires in the ceiling with luminaires indicated in a lighting plan and ensure that said luminaire is hard wired to whichever switch has also been indicated on the plan as being the control point for that lamp. In the case of traditionally wired systems this process is slow and laborious. Situations become more difficult when it becomes desirable to control traditionally wired luminaries by wireless means. In this case it becomes necessary for the installation engineer to record the unique wireless identifier (ID number) associated with each luminaire and to transfer that information to the lighting plan. When wireless lighting controls, such as switches, are then installed, it similarly becomes necessary to transfer the switch ID details to the lighting plan. The next step in the process is typically to manually create a binding table somewhere in the control system to associate switches with luminaires. Finally, the system needs to be tested to ensure that the desired binding have been allocated correctly.
Therefore, it is desirable to simplify the controller-luminaire mapping process. For example, the luminaire and control point mapping process could be automated, if the physical location of every luminaire in the ceiling was provided to the system.
Currently, many conventional technical solutions for locating objects employ wireless technologies, such as ZigBee or WiFi. Within this general category of solutions, the two most common systems to be found are either signal strength based or time of flight based.
Radio location systems that use signal strength as the basis for their measurement, for example those produced by AeroScout and Ekahau, are generally relatively easy to implement at modest cost, but have rather poor intrinsic accuracy, varying by perhaps five meters from of the true location. Accuracy can be improved with a technique known as finger printing, which involves measuring the signal strength at every point in a room in advance. However, the process is laborious to carry out and the resulting finger print profile may change with minor alterations within the room, for example moving furniture.
Location systems based on time of flight, such as those, for example, developed by UbiSense of Cambridge, United Kingdom, can achieve much greater accuracy than signal strength based alternatives, however, they are complex and expensive to implement, and can still suffer from accuracy or reliability problems due to propagation effects such as multipath or fading. EMerge supports wireless communication with each luminaire on the DC grid. Such communication may be used to control functions of each luminaire, for example, on/off state, intensity and color selection. However, it may be costly and cumbersome to equip each luminaire with a wireless transceiver and to configure wireless communication with each luminaire.
Thus, there is a need in the art to simply and cost effectively obtain and monitor the location of luminaires in a lighting system. Further there is a need for simpler and more cost effective control communication with luminaires in a lighting system.